The invention pertains to the fields of fluid handling and electroosmotic flow. More particularly, the invention pertains to variable potential electrokinetic devices useful as pumps and flow controllers.
Electrokinetic pumps are useful for pumping fluids in a highly controllable manner. In addition, electrokinetic pumps provide advantages over mechanical pumps because the electrokinetic pumps may be manufactured with few or no moving parts. U.S. Pat. Nos. 6,013,164 and 6,019,882 describe the manufacture and use of the first electrokinetic pumps capable of generating pressures in excess of a few pounds per square inch (“psi”).
Electrokinetic flow controllers are useful for managing the flow of fluids through conduits and also have the advantage that they may be manufactured with few or no moving parts. U.S. patent application Ser. No. 09/942,884 assigned to Eksigent Technologies LLC describes the manufacture and use of the first electrokinetic flow controllers.
Notwithstanding these advantages, prior art electrokinetic pumps and flow controllers suffer from one or more shortcomings with respect to fluid composition, operating voltages, voltages at connection points to other devices, and pumping efficiencies that limit their use in many fluid handling applications.
U.S. Pat. No. 3,427,978 by Hanneman et al. discloses an electrohydraulic transducer designed to work with a purified, non-aqueous liquid having a hydrocarbon portion and a polar group and having a dielectric constant between 5 and 100. Furthermore, the devices taught by Hanneman et al. include in the pumping fluid a small amount of redox material so that the oxidation occurring at the anode balances the reduction occurring at the cathode thereby enabling the composition of the ionizing liquid to remain in an operationally stable condition over a period of a number of hours during the continuous application of an electrical potential difference of 200 volts and higher across the electrodes.
U.S. Pat. No. 6,171,067 to Parce provides a micropump that utilizes electroosmotic pumping of fluid in one conduit or region to generate a pressure based flow of material in a connected conduit, where the connected conduit has substantially no electroosmotic flow generated. The devices taught by Parce typically are fabricated using open microscale conduits, and include conduit wall surfaces that have associated charged functional groups to produce sufficient electroosmotic flow to generate requisite pressures in those conduits in which no electroosmotic flow is taking place. Parce also teaches that electroosmotic flow preferably is avoided in the first conduit portion either by providing the first conduit portion with substantially no net surface charge to propagate electroosmotic flow, or alternatively and preferably, electroosmotic flow is avoided in the first conduit portion by applying substantially no voltage gradient across the length of this conduit portion.
Takamura et al. (“Low-Voltage Electroosmosis Pump and Its Application to On-Chip Linear Stepping Pneumatic Pressure Source,” in J. M. Ramsey and A. van den Berg (eds.), Micro Total Analysis Systems 2001, pp. 230-232 (2001) Kluwer Academic Publishers, the Netherlands)(which reference is not admitted by applicants to be prior art to the present invention) teach low-voltage electroosmotic flow pumps consisting of narrow conduits and cascade configuration microfabricated on quartz chips. Takamura et al. do not teach, as their FIG. 4 illustrates, how to design and build pumps capable of generating pressures more than about 80 mm H2O (0.1 psi) or 4 mm H2O/volt (0.006 psi/volt), nor do they teach how to within broad limits arbitrarily set the potential at the inlet and outlet connection points of their electroosmotic pump.
The present invention addresses these and other shortcomings of the prior art by providing variable potential electroosmotic devices such as pumps capable of operation over a wide range of fluid composition and operating voltages, that can be fabricated as micro- or macro-scale devices, that are capable of generating considerably greater pressures/volt as compared to the prior art devices, and that can be configured for improved device safety and compatibility by allowing for the control of applied voltage at either or both of the ends of the devices. The present invention also provides improved geometries to enhance performance, safety and compatibility of electroosmotic flow controllers such as those described in co-owned U.S. patent application Ser. No. 09/942,884.